1. Field of the Invention
The present application relates to a method for producing a microstructure.
2. Description of the Related Art
Grids having periodic structures are used as spectrometer elements in various types of apparatus. In particular, a shield grating made of a metal having a high X-ray absorptance is used for nondestructive inspection, medical practice and the like.
The shield grating used in an X-ray Talbot interferometer is one of the exemplary shield gratings.
The X-ray Talbot interferometry is one of the imaging methods using X-ray phase contrast (X-ray phase imaging methods).
The X-ray Talbot interferometry will be simply described below.
In an X-ray Talbot interferometer, spatially coherent X-rays pass through a test object and a diffraction grating capable of diffracting X-rays to form an interference pattern.
A shield grating adapted to periodically block X-rays is located at the position where the interference pattern is formed, thus forming a moire pattern. This moire pattern is detected with a detector, and the information of the test object is collected from the detection result. In Talbot-Lau interferometer, which is a type of the Talbot interferometer, an X-ray shield grating is used to form a virtual state in which very small X-ray sources are arranged, thereby enhancing the X-ray spatial coherence of X-rays.
A typical shield grating used for the Talbot interferometry has a structure in which X-ray transmitting portions and X-ray shielding portions are periodically arranged.
The shielding portions are often defined by a metal structure including main portions having a high aspect ratio, made of a metal having a high X-ray absorptance, such as gold, wherein the aspect ratio refers to the ratio (h/w) of the height or depth of a structure to the width thereof. For forming a shield grating including shielding portions defined by such a metal structure, Japanese Patent Laid-Open No. 2010-185728 discloses a method including the operation of filling a mold with a metal by plating. In this patent document, the mold is prepared by forming a groove in a silicon body by reactive etching. The shield grating is formed by depositing a metal in the groove by plating.
In this method, however, the X-ray transmitting portions of the shield grating are formed of silicon.
Silicon has a lower X-ray absorptance than X-ray absorbing metals such as gold. It is however not 0 and silicon absorbs X-rays.
Consequently, the contrast between the amount of X-rays transmitted through the shielding portions and the amount of X-rays transmitted through the transmitting portions (hereinafter may be referred to as X-ray blocking contrast) can be reduced, or the amount of X-rays reaching the detector can be reduced.